Re: [RFC PATCH] target/ppc: Add capability for enabling secure guests

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Mar 20, 2020 at 08:23:53PM -0300, Fabiano Rosas wrote:
> Making use of ppc's Protected Execution Facility (PEF) feature, a
> guest can become a secure guest (aka. secure VM - SVM) and have its
> memory protected from access by the host. This feature is mediated by
> a piece of firmware called the Ultravisor (UV).
> 
> The transition from a regular to a secure VM is initiated by the guest
> kernel during prom_init via the use of an ultracall (enter secure mode
> - UV_ESM) and with cooperation from the hypervisor via an hcall
> (H_SVM_INIT_START).
> 
> Currently QEMU has no knowledge of this process and no way to
> determine if a host supports the feature. A guest with PEF support
> enabled would always try to enter secure mode regardless of user
> intent or hardware support.
> 
> To address the above, a new KVM capability (KVM_CAP_PPC_SECURE_GUEST
> [1]) is being introduced in the kernel without which KVM will block
> the secure transition.
> 
> This patch adds support for checking/enabling this KVM capability via
> a new spapr capability (SPAPR_CAP_SECURE_GUEST) and the equivalent
> command line switch (-machine pseries,cap-svm). The capability
> defaults to off.
> 
> 1- https://lore.kernel.org/kvm/20200319043301.GA13052@blackberry
> 
> Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
> ---
> 
> I have implemented this to be able to test Paul's patch. I'm sending
> it as RFC in case it helps anyone else and if we decide to go in this
> direction I can develop it further.

LGTM

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

It will miss the qemu-5.0 cut-off, of course, but that should be ok.

> 
> PS: TCG currently gets in a loop of 0x700 due to the lack of 'sc 2'
> emulation - and all the rest of PEF, of course =).
> 
> ---
>  hw/ppc/spapr.c         |  1 +
>  hw/ppc/spapr_caps.c    | 30 ++++++++++++++++++++++++++++++
>  include/hw/ppc/spapr.h |  3 ++-
>  target/ppc/kvm.c       | 12 ++++++++++++
>  target/ppc/kvm_ppc.h   | 12 ++++++++++++
>  5 files changed, 57 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 9a2bd501aa..a881ac4e29 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -4542,6 +4542,7 @@ static void spapr_machine_class_init(ObjectClass *oc, void *data)
>      smc->default_caps.caps[SPAPR_CAP_LARGE_DECREMENTER] = SPAPR_CAP_ON;
>      smc->default_caps.caps[SPAPR_CAP_CCF_ASSIST] = SPAPR_CAP_ON;
>      smc->default_caps.caps[SPAPR_CAP_FWNMI] = SPAPR_CAP_ON;
> +    smc->default_caps.caps[SPAPR_CAP_SECURE_GUEST] = SPAPR_CAP_OFF;
>      spapr_caps_add_properties(smc, &error_abort);
>      smc->irq = &spapr_irq_dual;
>      smc->dr_phb_enabled = true;
> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
> index 679ae7959f..375b7e0b30 100644
> --- a/hw/ppc/spapr_caps.c
> +++ b/hw/ppc/spapr_caps.c
> @@ -524,6 +524,27 @@ static void cap_fwnmi_apply(SpaprMachineState *spapr, uint8_t val,
>      }
>  }
> 
> +static void cap_secure_guest_apply(SpaprMachineState *spapr,
> +                                   uint8_t val, Error **errp)
> +{
> +    if (!val) {
> +        /* capability disabled by default */
> +        return;
> +    }
> +
> +    if (!kvm_enabled()) {
> +        error_setg(errp, "No PEF support in tcg, try cap-svm=off");
> +        return;
> +    }
> +
> +    if (!kvmppc_has_cap_secure_guest()) {
> +        error_setg(errp, "KVM implementation does not support secure guests, "
> +                   "try cap-svm=off");
> +    } else if (kvmppc_enable_cap_secure_guest() < 0) {
> +        error_setg(errp, "Error enabling cap-svm, try cap-svm=off");
> +    }
> +}
> +
>  SpaprCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
>      [SPAPR_CAP_HTM] = {
>          .name = "htm",
> @@ -632,6 +653,15 @@ SpaprCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
>          .type = "bool",
>          .apply = cap_fwnmi_apply,
>      },
> +    [SPAPR_CAP_SECURE_GUEST] = {
> +        .name = "svm",
> +        .description = "Allow the guest to become a Secure Guest",
> +        .index = SPAPR_CAP_SECURE_GUEST,
> +        .get = spapr_cap_get_bool,
> +        .set = spapr_cap_set_bool,
> +        .type = "bool",
> +        .apply = cap_secure_guest_apply,
> +    },
>  };
> 
>  static SpaprCapabilities default_caps_with_cpu(SpaprMachineState *spapr,
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index 42d64a0368..7f5289782d 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -81,8 +81,9 @@ typedef enum {
>  #define SPAPR_CAP_CCF_ASSIST            0x09
>  /* Implements PAPR FWNMI option */
>  #define SPAPR_CAP_FWNMI                 0x0A
> +#define SPAPR_CAP_SECURE_GUEST          0x0B
>  /* Num Caps */
> -#define SPAPR_CAP_NUM                   (SPAPR_CAP_FWNMI + 1)
> +#define SPAPR_CAP_NUM                   (SPAPR_CAP_SECURE_GUEST + 1)
> 
>  /*
>   * Capability Values
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 597f72be1b..9254749cd7 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -88,6 +88,7 @@ static int cap_ppc_safe_indirect_branch;
>  static int cap_ppc_count_cache_flush_assist;
>  static int cap_ppc_nested_kvm_hv;
>  static int cap_large_decr;
> +static int cap_ppc_secure_guest;
> 
>  static uint32_t debug_inst_opcode;
> 
> @@ -135,6 +136,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>      cap_resize_hpt = kvm_vm_check_extension(s, KVM_CAP_SPAPR_RESIZE_HPT);
>      kvmppc_get_cpu_characteristics(s);
>      cap_ppc_nested_kvm_hv = kvm_vm_check_extension(s, KVM_CAP_PPC_NESTED_HV);
> +    cap_ppc_secure_guest = kvm_vm_check_extension(s, KVM_CAP_PPC_SECURE_GUEST);
>      cap_large_decr = kvmppc_get_dec_bits();
>      /*
>       * Note: setting it to false because there is not such capability
> @@ -2532,6 +2534,16 @@ int kvmppc_enable_cap_large_decr(PowerPCCPU *cpu, int enable)
>      return 0;
>  }
> 
> +bool kvmppc_has_cap_secure_guest(void)
> +{
> +    return !!cap_ppc_secure_guest;
> +}
> +
> +int kvmppc_enable_cap_secure_guest(void)
> +{
> +    return kvm_vm_enable_cap(kvm_state, KVM_CAP_PPC_SECURE_GUEST, 0, 1);
> +}
> +
>  PowerPCCPUClass *kvm_ppc_get_host_cpu_class(void)
>  {
>      uint32_t host_pvr = mfpvr();
> diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
> index 332fa0aa1c..a9a3aa67c6 100644
> --- a/target/ppc/kvm_ppc.h
> +++ b/target/ppc/kvm_ppc.h
> @@ -72,6 +72,8 @@ int kvmppc_set_cap_nested_kvm_hv(int enable);
>  int kvmppc_get_cap_large_decr(void);
>  int kvmppc_enable_cap_large_decr(PowerPCCPU *cpu, int enable);
>  int kvmppc_enable_hwrng(void);
> +bool kvmppc_has_cap_secure_guest(void);
> +int kvmppc_enable_cap_secure_guest(void);
>  int kvmppc_put_books_sregs(PowerPCCPU *cpu);
>  PowerPCCPUClass *kvm_ppc_get_host_cpu_class(void);
>  void kvmppc_check_papr_resize_hpt(Error **errp);
> @@ -380,6 +382,16 @@ static inline int kvmppc_enable_cap_large_decr(PowerPCCPU *cpu, int enable)
>      return -1;
>  }
> 
> +static inline bool kvmppc_has_cap_secure_guest(void)
> +{
> +    return false;
> +}
> +
> +static inline int kvmppc_enable_cap_secure_guest(void)
> +{
> +    return -1;
> +}
> +
>  static inline int kvmppc_enable_hwrng(void)
>  {
>      return -1;

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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